The present invention relates to paper making machines, and in particular to a paper tailing device for transferring a leading end of an initial portion of a paper web across a gap in a paper making machine during guiding of the web through the machine.
In making paper, a damp web of paper from a press section is carried through a drying section that includes heated rolls around which the web wraps for being heated and dried. As long as the web is continuous, it guides itself through the dryer. However, upon start-up of paper making or should the web break, it is necessary to guide an initial portion of or to thread the web through the drying section. Conventionally, threading is accomplished by gripping a side edge of the web between a pair of overlapping carrier ropes that run in sheaves alongside the path of travel of the web and guide the web from an inlet to an outlet of the drying section. Once the web is guided through the dryer, the dryer tensions the web and causes its edge to move from between the carrier ropes as the web shifts to its normal run position.
Paper drying sections often have a calibrating head that moves within a gap transversely across and beyond the edges of the web to sense web moisture, thickness, etc.. Conventionally, the carrier ropes for guiding the web through the drying section extend alongside the path of travel of the web through the dryer. The arrangement must therefore be such that the carrier ropes do not interfere with or block movement of the calibrating head while the dryer is operating.
According to one prior technique, a single pair of carrier ropes is used to guide the web through the drying section. The carrier ropes extend across a space at the end of the gap into which the calibrating head moves, and after the web is guided through the dryer the ropes are cut to accommodate unimpeded movement of the calibrating head into the space during operation of the dryer. This technique necessitates replacing the carrier ropes on the drying section each time that a web is to be guided through the dryer.
According to another prior technique, two pairs of carrier ropes are used to guide the web through the drying section. One pair of ropes leads to and defines an outgoing nip on one side of the gap traversed by the calibrating head, and the other pair leads away from and defines an incoming nip on the other side of the gap. The outgoing and incoming nips are spaced apart by at least the width of the gap to accommodate unimpeded movement of the calibrating head during operation of the dryer. In consequence, the incoming nip is spaced sufficiently far from the outgoing nip that the leading end of the web is not automatically introduced into the incoming nip as the web is guided through the dryer, as a result of which the web, upon exiting the outgoing nip, falls through the gap into a broke pit until an operator is able to manually introduce the web into the incoming nip.